Dana M. Hurley

LRO-LAMP observations of the LCROSS impact plume.

Watering the Moon About a year ago, a spent upper stage of an Atlas rocket was deliberately crashed into a crater at the south pole of the Moon, ejecting a plume of debris, dust, and vapor. The goal of this event, the Lunar Crater Observation and Sensing Satellite (LCROSS) experiment, was to search for water and other volatiles in the soil of one of the coldest places on the Moon: the permanently shadowed region within the Cabeus crater. Using ultraviolet, visible, and near-infrared spectroscopy data from accompanying craft, Colaprete et al. (p. 463; see the news story by Kerr; see the cover) found evidence for the presence of water and other volatiles within the ejecta cloud. Schultz et al. (p. 468) monitored the different stages of the impact and the resulting plume. Gladstone et al. (p. 472), using an ultraviolet spectrograph onboard the Lunar Reconnaissance Orbiter (LRO), detected H2, CO, Ca, Hg, and Mg in the impact plume, and Hayne et al. (p. 477) measured the thermal signature of the impact and discovered that it had heated a 30 to 200 square-meter region from ∼40 kelvin to at least 950 kelvin. Paige et al. (p. 479) mapped cryogenic zones predictive of volatile entrapment, and Mitrofanov et al. (p. 483) used LRO instruments to confirm that surface temperatures in the south polar region persist even in sunlight. In all, about 155 kilograms of water vapor was emitted during the impact; meanwhile, the LRO continues to orbit the Moon, sending back a stream of data to help us understand the evolution of its complex surface structures. A controlled spacecraft impact into a crater in the lunar south pole plunged through the lunar soil, revealing water and other volatiles. On 9 October 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) sent a kinetic impactor to strike Cabeus crater, on a mission to search for water ice and other volatiles expected to be trapped in lunar polar soils. The Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) observed the plume generated by the LCROSS impact as far-ultraviolet emissions from the fluorescence of sunlight by molecular hydrogen and carbon monoxide, plus resonantly scattered sunlight from atomic mercury, with contributions from calcium and magnesium. The observed light curve is well simulated by the expansion of a vapor cloud at a temperature of ~1000 kelvin, containing ~570 kilograms (kg) of carbon monoxide, ~140 kg of molecular hydrogen, ~160 kg of calcium, ~120 kg of mercury, and ~40 kg of magnesium.

Particle Emissions from Aircraft Engines–A Survey of the European Project PartEmis

An overview of the goals and achievements of the European PartEmis project (Measurement and prediction of emissions of aerosols and gaseous precursors from gas turbine engines) is presented. PartEmis was focussed on the characterisation and quantification of exhaust emissions from a gas turbine engine. The engine was composed of a combustor and a unit to simulate a 3-shaft turbine section (so-called Hot End Simulator; HES). A comprehensive suite of aerosol, gas and chemi-ion measurements were conducted under different, i) combustor and HES operating conditions, ii) fuel sulphur concentrations. Measured aerosol properties were mass and number concentration, size distribution, mixing state, thermal stability of internally mixed particles, hygroscopicity, cloud condensation nuclei (CCN) activation potential, and chemical composition. Furthermore, chemi-ions, non-methane volatile organic compounds (NMVOCs) and OH were monitored. The combustor operation conditions corresponded to modern and older engine gas path temperatures at cruise altitude, with fuel sulphur contents (FSC) of 0.05, 0.41, and 1.270 g kg −1 . The combustor behaved like a typical aircraft engine combustor with respect to thermodynamic data and main emissions, which suggests that the PartEmis database may be applicable to contemporary aircraft engines. The conclusions drawn from the PartEmis experiment are discussed separately for combustion particles, ultrafine particles, sulphate-containing species and chemi-ions, particle hygrioscopic growth and CCN activation, gaseous organic fraction, and emission properties. Zusammenfassung Die in dem europaischen Projekt PartEmis (Messung und Modellierung der Emissionen von Partikeln und gasformigen Vorlaufern aus Gasturbinen) erzielten Ergebnisse werden vorgestellt. PartEmis konzentrierte sich auf die Charakterisierung und Quantifizierung von Abgasemissionen aus einer Gasturbine. Das Triebwerk bestand aus einer Brennkammer und einer Einheit zur Simulierung einer 3-stufigen Turbinensektion, dem so genannten Hot End Simuator. Ein umfassendes System zur Messung von Aerosolen, Gasen und Ionen wurde i) unter verschiedenen Betriebsbedingungen der Brennkammer und des Hot End Simulators, und ii) bei verschiedenen Schwefelgehalten im verwendeten Treibstoff eingesetzt. Die gemessenen Aerosoleigenschaften umfassten Massen- und Anzahlkonzentration, Grosenverteilung, Mischungszustand, thermische Stabilitat intern gemischter Partikel, Hygroskopizitat, Aktivierbarkeit zur Bildung von Wolkentropfen, und chemische Zusammensetzung. Weiterhin wurden Chemi-Ionen, Nicht-Methan Kohlenwasserstoffe (NMVOC) und OH gemessen. Die Betriebsbedingungen der Brennkammer entsprachen den Gaseintrittstemperaturen alter und moderner Triebwerke in Reiseflughohe. Der Schwefelgehalt im Treibstoff variierte von 0,05 uber 0,41 bis 1,270 g kg −1 . Die Brennkammer verhielt sich im Bezug auf thermodynamische Daten und Emissionsdaten wie die typische Brennkammer eines Flugzeugtriebwerks. Davon ausgehend lassen sich die erreichten Ergebnisse auf moderne Flugzeugtriebwerke ubertragen. Die Schlussfolgerungen aus dem PartEmis Experiment werden getrennt fur Verbrennungspartikel, ultrafeine Partikel, sulfathaltige Komponenten und Chemi-Ionen, Feuchtewachstum der Partikel und Aktivierbarkeit zu Wolkentropfen, gasformige organische Verbindungen und Emissionseigenschaften der Brennkammer diskutiert.

Temporal variability of lunar exospheric helium during January 2012 from LRO/LAMP

Abstract We report observations of the lunar helium exosphere made between December 29, 2011, and January 26, 2012, with the Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph on NASA’s Lunar Reconnaissance Orbiter Mission ( LRO ). The observations were made of resonantly scattered He i λ 584 from illuminated atmosphere against the dark lunar surface on the dawn side of the terminator. We find no or little variation of the derived surface He density with latitude but day-to-day variations that likely reflect variations in the solar wind alpha flux. The five-day passage of the Moon through the Earth’s magnetotail results in a factor of two decrease in surface density, which is well explained by model simulations.

Grain‐scale supercharging and breakdown on airless regoliths

Interactions of the solar wind and emitted photoelectrons with airless bodies including asteroids and the Moon have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

The Statistical Mechanics of Solar Wind Hydroxylation at the Moon, Within Lunar Magnetic Anomalies, and at Phobos

We present a new formalism to describe the outgassing of hydrogen initially implanted by the solar wind protons into exposed soils on airless bodies. The formalism applies a statistical mechanics approach similar to that applied recently to molecular adsorption onto activated surfaces. The key element enabling this formalism is the recognition that the inter-atomic potential between the implanted H and regolith-residing oxides is not of singular value, but possess a distribution of trapped energy values at a given temperature, F(U, T). All subsequent derivations of the outward diffusion and H retention rely on the specific properties of this distribution. We find that solar wind hydrogen can be retained if there are sites in the implantation layer with activation energy values exceeding 0.5 eV. We especially examine the dependence of H retention applying characteristic energy values found previously for irradiated silica and mature lunar samples. We also apply the formalism to two cases that differ from the typical solar wind implantation at the Moon. First, we test for a case of implantation in magnetic anomaly regions where significantly lower energy ions of solar wind origin are expected to be incident with the surface. In magnetic anomalies, H retention is found to be reduced due to the reduced ion flux and shallower depth of implantation. Second, we also apply the model to Phobos where the surface temperature range is not as extreme as the Moon. We find the H atom retention in this second case is higher than the lunar case due to the reduced thermal extremes (that reduces outgassing).

Spillage of lunar polar crater volatiles onto adjacent terrains: The case for dynamic processes

We present an investigation of the release and transport of lunar polar crater volatiles onto topside regions surrounding the cold traps. The volatiles are liberated via surface energization processes associated with the harsh space environment, including solar wind plasma sputtering and impact vaporization. We find that some fraction of these volatiles can migrate from crater floors onto topside regions (those regions directly adjacent to and above the polar crater floors), and that these surrounding terrains should contain a sampling of the material originating within the crater itself. It is concluded that the nature of the volatile content on crater floors can be obtained by sampling the surface volatiles that have migrated or “spilled out” onto the adjacent terrain. This “spillage” effect could make human or robotic prospecting for crater resources significantly easier, since an assessment may not require direct entry into the very harsh polar crater environment. We also suggest that there are dynamic processes actively operating on the crater floors, and we estimate their source rates assuming dynamic equilibrium of the observed water frost and our modeled loss rates.

Direct evidence of surface exposed water ice in the lunar polar regions

Significance We found direct and definitive evidence for surface-exposed water ice in the lunar polar regions. The abundance and distribution of ice on the Moon are distinct from those on other airless bodies in the inner solar system such as Mercury and Ceres, which may be associated with the unique formation and evolution process of our Moon. These ice deposits might be utilized as an in situ resource in future exploration of the Moon. Water ice may be allowed to accumulate in permanently shaded regions on airless bodies in the inner solar system such as Mercury, the Moon, and Ceres [Watson K, et al. (1961) J Geophys Res 66:3033–3045]. Unlike Mercury and Ceres, direct evidence for water ice exposed at the lunar surface has remained elusive. We utilize indirect lighting in regions of permanent shadow to report the detection of diagnostic near-infrared absorption features of water ice in reflectance spectra acquired by the Moon Mineralogy Mapper [M (3)] instrument. Several thousand M (3) pixels (∼280 × 280 m) with signatures of water ice at the optical surface (depth of less than a few millimeters) are identified within 20° latitude of both poles, including locations where independent measurements have suggested that water ice may be present. Most ice locations detected in M (3) data also exhibit lunar orbiter laser altimeter reflectance values and Lyman Alpha Mapping Project instrument UV ratio values consistent with the presence of water ice and also exhibit annual maximum temperatures below 110 K. However, only ∼3.5% of cold traps exhibit ice exposures. Spectral modeling shows that some ice-bearing pixels may contain ∼30 wt % ice that is intimately mixed with dry regolith. The patchy distribution and low abundance of lunar surface-exposed water ice might be associated with the true polar wander and impact gardening. The observation of spectral features of H2O confirms that water ice is trapped and accumulates in permanently shadowed regions of the Moon, and in some locations, it is exposed at the modern optical surface.